Hi!
I read many nice thing about Pi wound output transformers.
I know that Pi wound transformers are 100% symmetrically balanced and have 2X greater high frequency response than a conventional layer wound output transformers.
Pi-winding helps to breakup series resonance at high frequencies. etc.
Does anybody have experience with this technique?
Is it realy works?

Hi!
I read many nice thing about Pi wound output transformers.
I know that Pi wound transformers are 100% symmetrically balanced and have 2X greater high frequency response than a conventional layer wound output transformers.
Pi-winding helps to breakup series resonance at high frequencies. etc.
Does anybody have experience with this technique?
Is it realy works?

It certainly works for tuning coils used at lower radio frequencies, like 100KHz-1MHz. By using a pie wound (not 'pi') coil, you reduce the parasitic capacitance across the coil for a given physical size, thus increasing its quality factor, Q. This is very important in many radio application, like when trying to make sharp bandpass filters.

Whether this makes any difference in audio transformers I cannot say...

I know where the "information" comes from.
As long as the claim is not backed up by reliable measurment with an audio transformer, it does not make sense.
The site has useful info and a bit of nonsense anyway.

Personally I prefer toroids. Unlike many contrary beliefs, it is not a problem to design and build audio output toroids which don't suffer from core saturation caused by DC imbalance of output stage idle current.

I have a pair of 60W 5K PP toroids which can sustain 15 mA imbalance at 36W/20 Hz (lover frequency = higher flux density). I didn't tested them yet at full load, need to build power resistor network first.

Many people are obsessed with exotic techniques, but simply put, this is not necessary. Its possible to build excellent transformer with either EI, Double C, or toroid. The rest is up to availability of material and price.

Pie winding reduces capacitance, so it raises the HF resonance frequency. It also reduces coupling, so fine for a choke (you can just add extra turns) but bad for a transformer. For audio purposes people use various interleaving tricks to maximise coupling; pie winding takes you in the wrong direction.